Do the homeowners know your brother? Do you live in the same neighborhood? If there is no connection and it is a completely random person, then he probably won't get caught even if you can see his face (unless the cameras got a license plate or some other identifier). So he shouldn't freak out too much.

If he does get caught, he could get a fine (not highly probably depending on age), and he might be able to work out some deal with the owners and police officer and your parents such as cleaning up the person's yard of the TP and apologizing at the worst.

If he is really that worried about it, he could just go to the person's house and confess to it and offer to clean it up.